<?php
namespace wxCrypt;

/**
 * 提供接收和推送给公众平台消息的加解密接口
 */
class Prpcrypt
{
	public $key;


	function __construct($k)
	{
		$this->key = base64_decode($k . '=');
	}


	/**
	 * 对明文进行加密
	 * @param string $text 需要加密的明文
	 * @return string 加密后的密文
	 */
	public function encrypt($text, $appid)
	{
		try
		{
			// 获得16位随机字符串，填充到明文之前
			$random = $this->getRandomStr();
			$text = $random . pack("N", strlen($text)) . $text . $appid;
			$iv = substr($this->key, 0, 16);
			// 使用自定义的填充方式对明文进行补位填充
			$pkc_encoder = new PKCS7Encoder;
			$text = $pkc_encoder->encode($text);
			$encrypted = openssl_encrypt($text, 'AES-256-CBC', $this->key, OPENSSL_RAW_DATA|OPENSSL_ZERO_PADDING, $iv);

			// 使用BASE64对加密后的字符串进行编码
			return [
				ErrorCode::$OK,
				base64_encode($encrypted)
			];
		}
		catch (Exception $e)
		{
			return [
				ErrorCode::$EncryptAESError,
				null
			];
		}
	}


	/**
	 * 对密文进行解密
	 * @param string $encrypted 需要解密的密文
	 * @return string 解密得到的明文
	 */
	public function decrypt($encrypted, $appid)
	{
		try
		{
			// 使用BASE64对需要解密的字符串进行解码
			$ciphertext_dec = base64_decode($encrypted);
			$iv = substr($this->key, 0, 16);
			$decrypted = openssl_decrypt($ciphertext_dec, 'AES-256-CBC', $this->key, OPENSSL_RAW_DATA|OPENSSL_ZERO_PADDING, $iv);
		}
		catch (Exception $e)
		{
			return [
				ErrorCode::$DecryptAESError,
				null
			];
		}

		try
		{
			// 去除补位字符
			$pkc_encoder = new PKCS7Encoder;
			$result = $pkc_encoder->decode($decrypted);
			// 去除16位随机字符串,网络字节序和AppId
			if(strlen($result) < 16)
			{
				return '';
			}
			$content = substr($result, 16, strlen($result));
			$len_list = unpack("N", substr($content, 0, 4));
			$xml_len = $len_list[1];
			$xml_content = substr($content, 4, $xml_len);
			$from_appid = substr($content, $xml_len + 4);
		}
		catch (Exception $e)
		{
			return [
				ErrorCode::$IllegalBuffer,
				null
			];
		}
		if($from_appid != $appid)
		{
			return [
				ErrorCode::$ValidateAppidError,
				null
			];
		}

		return [
			0,
			$xml_content
		];
	}


	/**
	 * 随机生成16位字符串
	 * @return string 生成的字符串
	 */
	function getRandomStr()
	{
		$str = '';
		$str_pol = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz';
		$max = strlen($str_pol) - 1;
		for($i=0; $i<16; $i++)
		{
			$str .= $str_pol[mt_rand(0, $max)];
		}
		return $str;
	}


}
